Currently, the IP mobility is becoming the focus for study. The IP mobility refers to maintaining the continuity of the existing session during movement. In other words, the mobile node changes its attachment point in the Internet without changing the IP address, thereby facilitating the mobile node to communicate with a corresponding node using the local address of the mobile node. There are many existing solutions for the IP mobility, as well as many classification manners. As classified by whether the terminal participating the mobility management process, there are two management manners: the terminal-based mobility management and the network-based mobility management. In the terminal-based mobility management, the terminal detects the mobility and initiates a signaling process to solve the mobility problem. The typical examples include the mobile IPv6 protocol. While in the network-based mobility management, the mobility management is mainly accomplished by the network entity through the signaling interaction process, in which the terminal is not required to participate. The typical examples include the agent mobile IP protocol.
In the prior art, a solution for the terminal-based IP mobility management is provided in Implementation and Evaluation of a Network-Controlled Mobility Management Protocol (IP2/MM): Performance Evaluation Compared with Mobile IPv6. In this terminal-based mobility management scheme, the mobile node (MN), i.e. the terminal, has two addresses: IP-host address (IPha) and IP-routing address (IPra). The IPha uniquely identifies a mobile node as the identifier of the mobile node, while the IPra represents the actual location of the mobile node as the locator of the mobile node.
The architecture of this mobility scheme is as illustrated in FIG. 1. This architecture includes an important mobility management entity, i.e. the Routing Manager (RM), which manages the mapping relations between the IPhas and IPras of the mobile nodes, as well as maintains the session information between the mobile nodes. When the mobile nodes communicate with each other, the transport layer protocol is identified with the IPha, and the IP layer also uses the IPha address as the source and the destination addresses of a message. Taking the entities as illustrated in FIG. 1 as an example, when MN2 sends a message to MN1, the IPha is employed as the IP address in the message. When the message arrives at the access router (AR) 2, AR2 converts the IPha in the message into IPra, and routes the message to AR1 on the opposite end by the IPra. The AR1 further converts the IPra address in the IP header into the IPha address, and then forwards the message to MN1 for processing.
In order to implement the message transfer process above, the ARs at the sending end and the receiving end (AR1 and AR2) each needs to maintain the mapping relations between the IPhas and IPras of the two mobile node (MN1 and MN2). Taking AR1 as an example, AR1 maintains the Cache for Source Terminal (CST) and Cache for Destination Terminal (CDT) of MN1, the CST containing the mapping relation between the IPha and IPra of MN1, while CDT containing the mapping relation between the IPha and IPra of MN2 which is in communication with MN1. Conversely, on AR2, the CST contains the mapping relation between the IPha and IPra of MN2, while the CDT contains the mapping relation between the IPha and IPra of MN1 which is in communication with MN2.
This mobility scheme mainly includes the several processes as follow: terminal activation process, session initiation process, switching process, etc. The terminal activation process and session initiation process will not be repeated here. In this mobility scheme, the process for switching the access routers is as illustrated in FIG. 2, when MN2 switches from AR2 to AR3, the following steps are performed:
Step 101: The data packet sent from MN2 is cached by AR3 first because the CDT of AR3 does not have a cache entry for MN1 when the switching just occurs;
Step 102: MN2 sends an activation message to AR3;
Step 103: AR3 allocates an IPra address to MN2, and notifies the RM of the IPha and the IPra addresses in an Activation Notification (AN) message;
Step 104: The RM updates the IPra address corresponding to MN2 in the cache entry;
Step 105: The RM sends an IP-routing address update (IPra updata, IPU) to AR1, instructing AR1 to update the IPra address corresponding to MN2;
Step 106: AR1 sends an IPU Ack message to the RM after updating the CDT, and the RM returns an IPU message to AR3;
Step 107: AR3 creates the CST about MN2 and the CDT about MN1, containing the IPhas and IPras of MN2 and MN1
Step 108: AR3 returns an Activation Ack message to MN2; and
Step 109: AR3 processes the data packet according to the address mapping in the CST and CDT. The subsequent process is the same as that after a session is established.
During the switching, because neither the AR3 stores the address mapping relations of MN2 and MN1, nor the AR1 stores the new address mapping relation of MN2, the activation process of MN2 is required to update the new address mapping relations of MN2 and MN1 into the cache entries of AR1, AR3 and RM. However, this process has a relatively long delay. It has been mentioned above that the data packet will be cached in AR3 during the switching, however, the data packet may be lost if the cache of AR3 is not enough during the switching.
Furthermore, the RM needs to store the session information between the mobile nodes while storing the address mapping relations between the IPhas and IPras of the mobile nodes. This session information may be used in the switching process for the RM to notify the access router on the opposite end according to the session information. Without the session information and the signaling interaction process, the switching operation may not be achieved. Assuming that there are m mobile nodes in the network, there will be m mapping relations between the IPhas and IPras corresponding to the mobile nodes. Therefore, the session number between the mobile nodes may be on the order of the square of m, far exceeding the number of the mapping relations between the IPhas and IPras stored simple for individual terminals. Thus, it is required that the RM should have a large storage capacity.